1. Field of the Invention
The present invention relates to a tool holder system for industrial cutting tools such as drills, boring tools, probes, and the like; and to an improved collet and collet holder for use in such system.
2. Description of the Prior Art
An industrial cutting tool apparatus conventionally includes a power drive unit, such as an electric, hydraulic or pneumatic motor; a suitable cutting tool, such as a drill, boring tool, probe or the like; and a tool holder for connecting the cutting tool to the power drive unit. The tool holder typically includes a socket or sleeve member which is mounted directly to the power drive unit and which is adapted to support the cutting tool in order to connect the tool to the power drive unit.
Usually, the socket is of a fixed size whereas the size of the tool may vary. Accordingly, it has become customary in the industry to provide intermediate bushings or collets to mount the tool to the socket. In particular, collets are provided which have a fixed external dimension sized to properly fit within the socket, but which have internal dimensions which vary so as to receive tools of different size.
In tool holder systems utilizing an intermediate collet, in order to ensure that the cutting tool is properly driven and maintained accurately aligned with the rotational axis of the power drive unit at all times; it is necessary to prevent the tool from slipping or otherwise moving within the collet; and, in addition, to prevent the collet from slipping or otherwise moving within the socket. This has been difficult to accomplish in a fully satisfactory manner, particularly with respect to securing the tool in the collet; and various collet structures have been developed in an effort to reliably support and hold the tool.
For example, in one common design, the collet includes a tapered axial bore for receiving the shank of the tool, and is provided with a plurality of longitudinal slits configured on the tapered inside diameter of the collet. A nut is secured onto the collet in such a manner as to cause the slits to be squeezed closed so as to compress the collet around the tool shank to grab and hold the tool.
In collets incorporating such design, however, the collet wears on the taper after a period of time resulting in a reduced holding force that can cause the tool to slip. Also, such collets tend to be inconsistently manufactured with respect to the accuracy of the taper and the like which can cause the tool to bottom out against the collet also resulting in tool slippage. Further, as the collet is compressed around the tool, the tool is often pushed off center or turned at an angle resulting in misalignment of the tool.
In another known design, a tool holder is ground on center to form a bore of a specific uniform diameter to receive the tool shank with minimal clearance. Set screws, for example two set screws, are then screwed into the tool holder against flats formed on the tool shank to lock the tool to the tool holder.
In this design, the locking screws can also push the tool off center as they are screwed into the tool holder resulting in an inaccurate alignment.
In general, current tool holder systems are not fully satisfactory in maintaining a cutting tool properly aligned with the axis of rotation of the power drive unit of an industrial cutting tool apparatus and of reliably holding the tool against slippage during use of the apparatus.